Multi-proxy identification of the Laschamp geomagnetic field excursion in Lake Pupuke, New Zealand

We present palaeomagnetic and cosmogenic radionuclide records of the Laschamp geomagnetic excursion in Lake Pupuke, a maar lake in Auckland, New Zealand. Laschamp was identified by a combination of relative palaeointensity, ¹⁰Be and ¹⁴C data from the lake sediments and represents the first such record from the Southern Hemisphere. Despite the high organic carbon content, which causes relatively weak natural remanent magnetisations, the geomagnetic intensity minimum associated with the Laschamp excursion is identifiable as a relative palaeointensity minimum that is synchronous with (i) a peak in ¹⁰Be concentration and (ii) an anomaly in Δ¹⁴C. The Lake Pupuke time scale, provided by ¹⁴C data calibrated with INTCAL09, places the ¹⁰Be maximum at the same time as a ¹⁰Be maximum in Greenland ice cores when secured to the GICC05 time scale. The central age of the Laschamp geomagnetic excursion in Lake Pupuke as defined by the ¹⁰Be prediction peak is c. 41kyr, which confirms its global application as a palaeomagnetic isochron. Anomalous palaeomagnetic directional data at c. 32kyr in the Lake Pupuke sediments may represent the Mono Lake geomagnetic excursion, but tephra layers caused by frequent eruptions in the Auckland volcanic field during this excursion probably disrupted the palaeointensity signal. The study highlights the value of combining traditional palaeomagnetic methods with measurements of cosmogenic radionuclides in the quest for accurate and precise geochronologies during MIS3, a time of rapid global climate change.